Well jeremysterling were not a expert but theres been a few miles on the bender road i know what your saying about the shoes we used to do that years ago .
But that was with the older models & types 555 not todays SB new after the day greenlee went digital read out on there hand controls and started the dual head combos its not wise to be changing parts around .
Sorry about the radius we use that a lot on our benders because we have no charts we have lots of benders and no charts.
Most of the guys have there own pocket book . Have you ever bent a 2 inch rigid with radi meaning on the 555 try 9 5/8" but you going to pull it up with both 90s facen up .
Just ADD this 9 5/8 " instead of deduct on you mark of a back to back then from this mark install it in shoe facen up meaning both are facen up in bender shoe its easy try it out let me know what you think .
THATS FOR RIGID ONLY
This is what we use radi for it makes b&b easy to install in benders& work with and bender we can find any thing from it .
Take care